The present invention relates generally to a powder actuated tool and, more specifically, to such a tool having means for indicating an overdriven condition of the tool and a novel clamp arrangement for the return dog for the tool.
A powder actuated tool of the type to which the present invention relates is designed to accept a nail at the forward end of the barrel and a cartridge at the breech end of the barrel. The tool is pressed against a work surface to release a safety mechanism and then fired. Tools of this type are disclosed in the following U.S. Pat. Nos. 3,066,302 to De Caro et al.; 3,494,125 to Robinson; 3,678,808 to Hsu et al. and 4,114,792 to Pomeroy.
As explained in the aforementioned Hsu et al. patent, it is desirable to provide in a tool of the type hereinabove described means for absorbing the energy of the piston to avoid bending or other damage occurring to the piston when the piston is overdriven. Overdrive of the piston occurs when the nail is driven into a relatively soft material. In the Hsu et al. patent, the aforementioned problem is solved by forming a tapered portion of the piston of a relatively softer metal than that of a stop member in the barrel which it engages so that when the piston is overdriven, energy is dissipated by extruding of the softer tapered portion of the piston. While this arrangement is generally satisfactory, it provides no indication to the operator that overdriving of the piston has occurred and, therefore, that replacement of the piston might be required. In another tool, a collapsible metal ring is utilized as the stop member which, when impacted by the piston during overdrive, is partially collapsed, but does not extrude or provide any indication of overdriving occurring. It is one object of the present invention to provide means for visually indicating that repeated overdriving of the piston of the tool has occurred.
In powder actuated tools of the type contemplated herein, a return dog is mounted in the wall of the barrel housing and extends through an elongated guide slot in the barrel which is slidable in the housing. The return dog serves to limit forward movement of the piston in the barrel when the barrel is thrown forwardly in the barrel housing to ready the tool for firing. The return dog is removable from the barrel housing to permit replacement of the barrel or piston therein when required. In the tool disclosed in the aforementioned De Caro et al. patent, the return dog is in the form of a plug threaded into an opening in the wall of the barrel housing. During continued use of the tool, the dog may unthread in its corresponding opening in the barrel housing causing it to loosen, potentially rendering the tool unsafe. The aforementioned Robinson and Pomeroy patents each discloses a return dog which is mounted on the barrel housing and spring biased into its inward blocking position. This arrangement is more reliable than a threaded plug but is relatively time consuming to disassemble to allow removal of the barrel and piston from the barrel housing of the tool when maintenance or repair is required. It is, therefore, another object of the present invention to provide a novel clamping means for the return dog of the tool which is reliable yet easy to disengage for removal of the dog from the barrel housing.